Stainless Steel knives. What the difference between 420 and 440?

January 27, 2016 @ 11:22am

Stainless steel is a popular class of material for knife blades because it resists corrosion and is easy to maintain. However, it is not impervious to corrosion or rust. In order for a steel to be considered stainless it must have a chromium content of at least 13%.

The principle of stainless steel is that in an oxidizing chemical environment the oxide (chromium and sometimes nickel and other metal oxides) is stable, and when in a reducing (shortage of oxygen) environment at least one metal is stable. This usually works, except in an acid environment. In order to be hardenable, knife steel can contain limited chromium and very little nickel. So, even though stainless, hard knife steel has limited resistance to corrosion.

Austenitic stainless retains its non-magnetic crystal structure at room temperature, usually because it has high nickel content. It is therefore not hardenable by heat treating as typical hard steels are. So as knife steel it depends on other hardening methods such as alloying elements and cold working. It is highly corrosion resistant.

400 series (Ruko)

The 400 series remains one of the most popular choices for knife makers because it is easy to sharpen and it is resistant to corrosion.

· 416 is very similar to 410 with the addition of sulfur to improve machinability.

· 420 has more carbon than 410, but less than 440. As such it is softer than 440, but has a higher toughness.

420 series contain 4 types, which is defined by its carbon content.

420A / 1.4021,

420B / 1.4024,

420C / 1.4034,

and 420D / 1.4037.

420D stainless steel has about 0.66 carbon content, this steel grade is widely used to make high end razor blades, surgical scalpels etc.

It obtains about 57 HRC after suitable heat treatment. 420HC ( 420C ) is a higher carbon content 420 stainless. The HC stands for "high carbon" and it can be brought to a higher hardness than 420 and should not be mistaken for it. 420A ( 420J1 ) and 420B ( 420J2 ) are economical, highly corrosion resistant stainless steel grades. Knife manufacturers use this material in budget knives, also in diving knives due to its high resistance to corrosion.

440B is almost identical to 440A, but has a higher carbon content range compared to 440A

440C is considered a high-end stainless steel. It is very resistant to corrosion and is one of the most common stainless alloys used for knife making

Benefits of Elements of Stainless Steels

Element

Increases
Edge
Retention

Increases
Hardness

Increases
Harden-
ability

Increases
Toughness

Increases
Tensile
Stength

Increases
Impact
Strength

Increases
Wear and
Abrasion
Resistance

Increases
Corrosion
Resistance

Carbon

x

x

x

x

Chromium

x

x

x

x

x

Manganese

x

x

x

Molybdenum

x

x

x

x

x

Nickel

x

x

Silicon

x

Vanadium

x

x

x

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